The present invention relates to adjustably controllable switches. It finds particular application in conjunction with capillary thermostat controlled switches for electric and gas ovens, and will be described with particular reference thereto. However, it is to be appreciated that the present invention will also find application in other thermostatic and pressure controls for use not only in home appliances, but also in industrial applications and the like.
Heretofore, range controls, i.e. thermostatic controls for the oven of a range, included a shaft adapted to receive the knob with which the consumer set the temperature of the oven. The shaft was commonly threadedly received in a metal mounting bracket such that rotation of the knob caused the shaft to travel longitudinally. Longitudinal movement of the shaft changed the bias, the mechanical advantage, or a neutral position of a lever arrangement. A bulb was positioned in the oven and connected by a capillary tube with a diaphragm that was also mounted to the bracket of the range control. As the bulb changed temperature, its contained air or other fluid expanded extending the diaphragm. The diaphragm extension interacted with the lever arrangement pivoting the lever to cause an electrical switch to change states. The electrical switch for an electric range was snap acting to permit higher current flows; whereas, for a gas oven, the switch was slow acting for more accurate temperature response at the expense of lower current carrying capacity.
One of the drawbacks of the prior art range controls resided in the difficulty and expense for calibration mechanisms. Temperature calibration was commonly adjusted by turning a threaded member in a threaded bore to adjust the rest position of the diaphragm. First, the pressure of the screwdriver or other tool on the threaded member added a temperature offset to the final calibration. Moreover, even with as many as 80 threads per inch, the amount of movement of the diaphragm assembly for calibration purposes was so small that a lever ratio of about 1:1 or at best 1.5:1 could be achieved. This low lever ratio limited the accuracy of the calibration.
Additional calibrations to the electrical switch, the shaft, and other parts of the control were also done with threaded members received in threaded bores. The cost of the threaded adjustment mechanisms was relatively high.
Another disadvantage of these prior art range controllers was that the threaded engagement of the shaft and bracket fixed the temperature adjustment. Each model required a different threaded shaft and bracket arrangement to accommodate different amounts of travel for different temperature ranges.
Another disadvantage of the prior art range controllers resided in the differing requirements for electric and gas ranges. A different electrical switch and actuator lever arrangement was required for the snap action of the electric range than for the slow acting switch of the gas range. This increased the necessary parts, inventory, and tooling requirements.
Another drawback of the prior art range controls resided in their cost. The prior art controls required numerous threaded members and mating threaded bores for temperature adjustment and calibration, all relatively expensive parts. The prior art range controllers also included numerous elements, such as the actuator lever assembly, which increased complexity and manufacturing cost. The additional parts, complexity, and calibration complexity required additional assembly operations, calibration checks, and the like.
The present invention contemplates a new and improved thermostatically or pressure actuated controller which overcomes the above-referenced problems and others.